Patient monitoring system

ABSTRACT

The patient monitoring system comprises at least one load cell element ( 12 ) mounted in relation to a support surface, the load cell element ( 12 ) determining movement of a person on a support surface. The movement is determined based on a reference ( 31 ) measured using the load cell element ( 12 ) when the person is positioned on the support surface in a reference position and the subsequent load changes determined using the load cell element in relation to the reference. If the load change exceeds a pre-defined threshold, an alarm ( 18 ) is activated. The user is able to set the threshold value of the alarm system according to the physical condition of the patient. For example, in some cases it is necessary to he notified about any movements and in others only major movements are of interest. The patient monitoring system is able to provide a flexible means of monitoring of a patient by a nurse or carer.

The invention relates to a patient monitoring system by detectingmovement of a person on a support surface, for example, a hospital bed.In a hospital where the individual is an injured or ill adult or childor in a nursing home where the individual is an elderly or senileperson, it is often desirable to know the level of activity of anindividual on the bed and to alert the nursing staff that the movementsof a patient have reached a level where attention is needed. Providingthe nursing staff with such information will improve their efficiencyand the quality of the patient care.

One common hospital accident is when a patient climbs out of a hospitalbed and is injured either by falling off the bed or by stumbling orfalling after successfully getting out of the bed. Essentially the sameconsiderations apply in nursing homes and other similar care facilities.In addition, there are numerous situations at home where it is desirableto know when an invalid, senile person or child is attempting to get outof bed.

The present invention can assist the nursing staff in their patientcare, by providing continuous information on a patient's movementcompared to a predetermined pattern of movement, and notify the staff ifthe movements of the patient exceeds the predetermined pattern.

This predetermined pattern of movement can be a simple function thatdetermines the movement of the patient by comparing a reference valuewith a fixed range. If the movement by the patient exceeds this rangethe nursing staff is notified.

Accordingly, the present invention comprises a patient monitoring methodby determining movement of a person on a support surface, including atleast one load cell element, wherein the movement is determined based ona reference measured using the load cell element when the person ispositioned on the support surface in a reference position and thesubsequent load changes determined using the load cell element inrelation to the reference.

Preferably, the movement is determined when the load changes in relationto the reference exceed a predefined threshold value. In this way, thenursing staff can monitor a patient recovering from a coma or when apatient starts to wake up and therefore starts to move by beingnotified, preferably by an alarm, when a predefined movement has takenplace.

Preferably, the predefined threshold value is adjustable. Therefore, itis possible to adjust the types of movements to be determined and toadjust the sensitivity of an alarm indicating that a predefined movementhas taken place. The present invention has the advantage that the careror nurse can decide the level of movement acceptable for any givenpatient before they need to intervene.

Preferably, the movement is monitored by determining the load and themonitoring the changes in the load measured by a load cell element.

In a preferred embodiment, the movement is determined as the differencebetween the load and the load reference.

The differences between the load and the load reference would show theperson's movements.

In another aspect, the present invention relates to a computer-readablemedium having stored therein instructions for causing a processing unitto execute a method as described above or preferably the method asdescribed above is embedded in a data processing system.

In a preferred embodiment, the invention relates to a movement detectionsystem to be mounted in relation to a support surface for determiningmovement of a person on the support surface, the system including atleast one load cell element to be mounted in relation to the supportsurface for measuring the load on the support surface, processing meansfor determining movement based on a relation between a load referencemeasured using the load cell element when the person is positioned onthe support surface in a reference position and the load determinedusing the load cell element.

Preferably, the load cell element is mounted on a frame supporting thesupport surface.

The invention will now be described by way of example and with referenceto the figures, where

FIG. 1 is a block diagram of a patient monitoring system which embodiesthe present invention and is incorporated into a hospital bed;

FIG. 2 illustrates a flow diagram of the method of movement detection ofa person on a support surface

FIGS. 3 a and 3 b illustrate graphs showing the load on a supportsurface with a person positioned on the support surface

Referring to FIG. 1, a hospital bed includes a rectangular patientsupporting frame, which is depicted diagrammatically at 10. The frame 10is itself conventional and not a part of the present invention, and istherefore not described in detail. The frame 10 normally supports amattress on which a patient rests.

The invention is described with respect to a bed frame 10 supported in aconventional manner by four load cells elements 12 at each corner of theframe 10, the invention is equally applicable to other bed frame andload cell element configurations. Each load cell element 12 produces anelectrical signal representative of the weight that it is supporting,including the weight of the frame 10, the mattress and any patientsupported on the frame. The total weight of the structure supported bythe load cell elements can be obtained by summing the respective weightvalues measured by the load cell elements. Advantageously, the presentinvention can use an existing weighing system and at least one of theload cell elements 12 for the patient monitoring system. Therefore anexisting weighing system can be further employed as a patient monitoringsystem. However, the patient monitoring system does not need a weighingsystem and can be operated as a stand alone system.

FIG. 2 illustrates a flow diagram of the method of patient monitoringaccording to the invention by determining movement of a person on asupport surface such as a support surface on a hospital bed 10comprising at least one load cell element 12.

The method can be implemented in a computer, and performed using thesame microprocessor 16 of the weighing system, if present or otherwiseand would in this case start with an initialisation 21, where constants,communication and hardware drivers were initialised.

The method comprises the step of measuring a load reference 31 by usingthe load cell element 12 when a person is positioned at the bed and ispositioned in a reference position. The load reference is obtained byreceiving a reference signal from the load cell element measuring theload reference.

Patient monitoring comprising the steps of measuring a current load 91using the load cell element 12, determining 70 the movement of theperson positioned at the hospital bed based on the change between thecurrent load and the stored load reference and based on the determinedmovement decide 30 whether or not the person positioned in the bed is indanger. This could be that the person has moved when he should not orhas moved too much or even is about to leave the bed. The danger pointis determined by testing whether or not the difference between thecurrent load and the load reference exceeds a predefined thresholdvalue. If the predefined threshold value is exceeded an alarm/warning 18is activated, and the monitoring is repeated until the threshold valueis exceeded.

The load cell element can be any means suitable for measuring a load ona surface, e.g. piezoelectric sensors or strain gauges or similar. In apreferred embodiment, two load cell elements are spaced at one end ofthe patient support surface, and the load change on each load cellelement is monitored in turn, for a period of one second each. If theload change in either of the load cell elements exceeds the pre-definedthreshold, an alarm is activated. The alarm system 18 can useinput/output devices, for example a keyboard or control panel 17 tocommunicate with the monitoring system. The user activates the alarmsystem via a control panel 17 when movements of a person positioned atthe bed need to be monitored.

The user positions the patient in a reference position and as describedin FIG. 1 receives a load reference from the load cell element 12. Theuser is then able to set the threshold value of the alarm systemaccording to the physical condition of the patient. For example, in somecases it is necessary to be notified about any movements and in othersonly major movements are of interest. Once the alarm system has beenactivated it will automatically start the monitoring as described inFIG. 1 and if the movement of the patient exceeds the set sensibilitylevel an alarm will start. The alarm 18 could for instance be a loudspeaker or a light that alerts the hospital staff. The alarm could be onthe support surface as well as remote from the support surface, forexample, on a central nurse station.

The patient monitoring system is able to provide a flexible means ofmonitoring of a patient by a nurse or carer. The nurse or carer canassess the degree of movement acceptable for a given patient and inputsthe appropriate threshold value on the control panel 17. In this way,the nurse is able to set any threshold value from a range correspondingto almost no movement of a patient to a patient moving freely around thebed to change their position within the bed and to operate the bedcontrols, phone, television, the alarm 18 sounding only if the patientleaves the bed. The present invention allows the nurse the flexibilityfor assessing each patient and setting a level of movement acceptablefor that patient before they need to intervene. Depending upon thepatient's treatment and health the nurse or carer may want to know whena patient has moved only slightly, or moved parts of the body, or when apatient is turning or shifting up or down the bed or is agitated andclimbing within or around the bed to finally exiting the bed.

FIGS. 3 a and 3 b illustrate graphs showing the asymmetric load L of asupport surface with a person positioned on the support surface measuredby a load cell element as a function of time t. The graphs illustratehow the load changes as a function of a person's movements on thesupport surface. The measured load changes when a person positioned atthe support surface moves, and the load cell element measures the loadasymmetrically.

The first measured load is used as a load reference and the followingloads measured illustrate how the load changes due to movements of theperson. The load measured increases in the region around 75 whichindicates that the person has moved to a position where more load isapplied to the load cell element, whereas the load has decreased inregion 77. In region 79 the load only changes incrementally about thelevel of the load reference; which indicates small movements of theperson. The movement of a person can be numerical expressed bydetermining the relation between the load reference and the currentload. This can be done by calculating the numerical load difference |LD|by subtracting the load reference from the current load and take thenumerical value of the result as illustrated in FIG. 3 b. The larger thenumerical load difference |LD|, the more movement of the person.Alternatively the load reference can be divided by the current loadresulting in a movement index, where an index equal to 1 indicates nomovement.

The threshold value can be defined as having an upper limit 71 and alower 73 limit. If these limits are exceeded an alarm is activated. Inthe illustrated graph an alarm would be activated in region 75 sincethese load values exceed the upper limit 71 and in region 77 where theload values exceed the lower limit 73. In order to avoid an alarmactivated on the basis of a single load value exceeding the thresholdvalue the method can be adjusted to activate the alarm when a number ofsuccessive load values have exceeded the threshold value. In FIG. 3 bonly an upper limit 71 is defined, as the numerical load differencecannot be less than zero. In region 75 an alarm will not be activated asthe number of successive load values exceeding the threshold value isnot larger than 3. However in region 77 the alarm will be activated bythe load value 76, as this is the fourth successive value that exceedsthe lower threshold value.

The movement of the person positioned at a support surface can also bedetermined by differentiating the graphs illustrated in FIG. 3 a or 3 b.The differentiated curves can be used to determine the activity of themovements. A large number of zero crossings of the differential curveindicate that the person changes position frequently. Furthermore largedifferential curves indicate that the person changes position very fast.

1-8. (canceled)
 9. A method for monitoring patient movement on a supportsurface including one or more weight sensors, the method including thesteps of: a. obtaining a reference load measurement from the weightsensors when the patient is situated on the support surface in areference position; b. subsequently obtaining current load measurementsfrom the weight sensors over time; and c. comparing each current loadmeasurement to the reference load measurement.
 10. The method of claim 9wherein a signal is triggered if the current load measurement and thereference load measurement differ by more than a predefined thresholdvalue.
 11. The method of claim 9 wherein: a. the current loadmeasurements are obtained at regular time intervals; and b. a signal istriggered if a predefined number of subsequent current load measurementsdiffer from the reference load measurement by more than a predefinedthreshold value.
 12. The method of claim 11 wherein: a. the weightsensors are provided in combination with a threshold control, and b.adjustment of the threshold control defines the threshold value.
 13. Themethod of claim 9 further including the steps of: a. determining thedifferences between successive current load measurements from eachweight sensor over time; and b. triggering a signal if the magnitude ofthe differences exceeds a predefined magnitude threshold value.
 14. Themethod of claim 9 further including the steps of: a. determining thedifferences between successive current load measurements from eachweight sensor over time; and b. triggering a signal if the frequency ofdifferences exceeding a predefined magnitude threshold value exceeds apredefined frequency threshold value.
 15. The method of claim 9 whereinthe current load measurements are obtained at regular time intervals.16. The method of claim 9 wherein the weight sensors are mounted on aframe supporting the support surface.
 17. The method of claim 9 whereinthe support surface includes two or more weight sensors spaced apartfrom each other.
 18. The method of claim 9 wherein: a. the supportsurface includes two or more weight sensors, and b. both: (1) thereference load measurement, and (2) the current load measurements, areeach obtained from all of the weight sensors in combination.
 19. Themethod of claim 9 wherein: a. the support surface includes two or moreweight sensors, and b. the step of obtaining current load measurementsover time includes obtaining load measurements from each of the weightsensors in turn.
 20. A method for monitoring patient movement on asupport surface including one or more weight sensors, the methodincluding the steps of: a. situating a patient on the support surfacewith the patient being in a reference position; b. recording a referenceload measurement from the weight sensors; c. setting a threshold valuedefining a degree of deviation from the reference load measurement; d.obtaining current load measurements from the weight sensors over time asthe patient moves from the reference position; and e. triggering asignal if the current load measurement and the reference loadmeasurement differ by more than the threshold value.
 21. The method ofclaim 20 wherein the current load measurements are obtained from each ofthe weight sensors on a periodic basis.
 22. The method of claim 21wherein the signal is triggered if a predefined number of successivecurrent load measurements from one or more of the sensors differs fromthe reference load measurement by more than the threshold value.
 23. Themethod of claim 21 wherein the signal is triggered if the differencesbetween the current load measurement and the reference load measurementalso change over some predefined number of successive current loadmeasurements.
 24. The method of claim 21 wherein the signal is triggeredif some predefined number of successive current load measurements areall different.
 25. The method of claim 21 wherein the signal istriggered if the differences between some predefined number ofsuccessive current load measurements are cumulatively greater than apredefined amount.
 26. A system for monitoring patient movement on asupport surface, the system including: a. at least one weight sensorsituated on or about the support surface; b. a processor: (1) obtainingcurrent load measurements from the weight sensor over time; (2)comparing each current load measurement to a predefined reference loadmeasurement; and (3) triggering a signal if the current load measurementand the reference load measurement differ by more than a predefinedthreshold value.
 27. The system of claim 26 wherein: a. two or moreweight sensors are situated on or about the support surface; and b. theprocessor repetitively cycles through the weight sensors in turn to: (1)obtain the current load measurement from each weight sensor; (2) comparethe current load measurement from each weight sensor to the predefinedreference load measurement; and (3) trigger the signal if the currentload measurement and the reference load measurement differ by more thana predefined threshold value.
 28. The system of claim 27 wherein theweight sensors are spaced about a frame supporting the support surface.